a. Field of the Invention
The present invention pertains generally to catheters that are used in the human body. More particularly, the present invention is directed to steerable catheters using flat pull wires to reduce the overall outer dimension of the catheter and a torque transfer layer made of braided flat wires and configured to provide increased strength, flexibility, and kink resistance.
b. Background Art
Catheters are used for an ever-growing number of procedures. For example, catheters are used for diagnostic, therapeutic, and ablative procedures, to name just a few examples. Typically, the catheter is manipulated through the patient's vasculature and to the intended site, for example, a site within the patient's heart. The catheter typically carries one or more electrodes, which may be used for ablation, diagnosis, or the like.
Many prior catheters use round wires as pull wires, and they typically either embed the wire directly into the catheter wall so that the pull wire and the lumen through which it runs are substantially the same size, or use a round wire to create a pull wire lumen and then place a smaller wire in the lumen as a pull wire. These conventional techniques and methods result in a catheter that is elliptical in its outer shape. An example of an elliptical catheter is disclosed and taught in U.S. Pat. No. 6,582,536, the contents of which are incorporated herein by reference.
As catheters are used in smaller and smaller passages, there is a growing need to use catheters that have a smaller outer dimension. Accordingly, there is a need to use steerable catheters that have smaller cross-sections.
It is known that, to facilitate placement of the diagnostic or therapeutic catheter at a location of interest within the patient, it may be introduced through another catheter, commonly known as a “guiding catheter” or “introducer catheter,” and the terms will be used interchangeably herein. Generally speaking, an introducer catheter is a tube having a high degree of directional control that is used to place other catheters, which may have little or no directional control, into specific areas of the patient's body.
In the field of cardiac ablation, for example, introducer catheters may be used to negotiate the patient's vasculature such that an ablation device may be passed therethrough and positioned to ablate arrhythmia-causing cardiac tissue. The introducer catheter itself may be advanced over a guide wire.
Generally, it is known that the introducer catheter must have an overall diameter small enough to negotiate blood vessels while retaining an inner diameter (or “bore size”) large enough to accommodate the ablation device therethrough. Furthermore, since the path within the patient is often long and tortuous, steering forces must be transmitted over relatively great distances. Accordingly, it is desirable for the introducer catheter to have sufficient axial strength to be pushed through the patient's vasculature via a force applied at its proximal end (“pushability”). It is also desirable for the introducer catheter to transmit a torque applied at the proximal end to the distal end (“torqueability”). An introducer catheter should also have sufficient flexibility to substantially conform to the patient's vasculature and yet resist kinking as it does so. One of ordinary skill in the art will recognize that these various characteristics are often in tension with one another, with improvements in one requiring compromises in others. For example, increasing the bore size of an introducer catheter having a given overall diameter requires utilizing a thinner wall. A thin-walled introducer, however, is more likely to collapse upon itself when a torque is applied at its proximal end.
To improve pushability, torqueability, flexibility, and kink resistance, many extant introducer catheters utilize one or more reinforcing layers in their construction. For example, the guiding catheter disclosed in U.S. Pat. No. 4,817,613 to Jaraczewski et al. (“Jaraczewski”) includes a pair of braided torque transmitting layers sandwiched between a flexible tubular member and a flexible plastic casing applied as a viscous material and subsequently cured. Jaraczewski also teaches, however, that to a certain degree, flexibility comes at the expense of torqueability. Further, depending on the thickness of the torque transfer layers, they may increase the wall thickness, thereby either increasing the overall diameter of the introducer catheter for a given bore size or decreasing the bore size for a given overall diameter.
Many extant large bore introducers (i.e., an introducer catheter with bore size of greater than about 6 French), in order to find a suitable balance of pushability, torqueability, flexibility, and kink resistance, have outer layers that are relatively stiff, which compromises torqueability, kink resistance, and flexibility for pushability.